2
advanced-math

A tunnel is shaped like a parabola y=−0.2x2+5y = -0.2x^2 + 5. How wide is the tunnel at the base (y=0y=0)?

A

10 m

B

5 m

C

25 m

D

20 m

Correct Answer: A

Choice A is the correct answer. Find the x-intercepts.

  1. −0.2x2+5=0-0.2x^2 + 5 = 0.
  2. 0.2x2=50.2x^2 = 5.
  3. x2=25x^2 = 25.
  4. x=±5x = \pm 5.
  5. Width = Distance between -5 and 5 = 5−(−5)=105 - (-5) = 10 meters.

Choice B is incorrect because it is the half-width. Choice C is incorrect. Choice D is incorrect.

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Set 19: Quadratic Equations and Functions 19